Drivers of Pancreatic Cancer: Beyond the Big 4

Background: Pancreatic cancer is frequently identified as the cancer type with the shortest probable survival time after diagnosis, and efforts to develop successful treatments have had a very limited impact in the clinic. One reason for the limited therapeutic options is the lack of appealing drug targets. The great majority of pancreatic cancers are classified as Pancreatic Ductal Adenocarcinoma (PDAC), in which the genetic landscape is dominated by four genes: KRAS, TP53, CDKN2A, and SMAD4. However, despite extensive knowledge of these genetic drivers, the development of effective therapies has seen only very limited success. Methods: Existing evidence indicates that mutations in the tumour suppressor gene PTEN are uncommon in PDAC (<10% cases). However, the loss of PTEN function through non-genetic mechanisms may be much more common and have a strong impact. We therefore summarise and review a large body of immunohistochemical studies that address the loss of PTEN in PDAC as well as a smaller number of studies addressing other implicated proteins, including KDM6A and ARID1A. Results: These studies show some loss of PTEN protein in more than half of PDAC cases. Furthermore, although genetic changes in genes including KDM6A/UTX and ARID1A are also uncommon, reduced expression of their encoded proteins is observed in many, perhaps most, cases of PDAC. Conclusions: These analyses, which go beyond genetics, highlight the broader set of cellular functions that are dysregulated in many pancreatic cancers and provide broader opportunities for treatment strategies. This review highlights the emerging importance of other drivers in PDAC, which are less well-studied in this context.